In recent years, the demand for the performance of photographic silver halide emulsions has become severe; in particular with respect to toughness, such as abrasion-and-pressure resistance, in audition to such photographic properties as high sensitivity and excellent graininess, a further high level is demanded.
It is considered preferable that, in order to make silver halide grains highly sensitive and to improve the abrasion-and-pressure resistance, the silver iodide (iodide ions) content should be uniform from grain to grain, with a view to effecting uniform chemical sensitization.
Conventionally, when a silver halide phase containing silver iodide is formed in a step of forming silver halide grains, the following methods for supplying iodide ions are used: a method wherein an aqueous iodide solution, such as an aqueous KI solution, is used; and a method disclosed in JP-A ("JP-A" means unexamined published Japanese patent application) No. 68538/1990, wherein silver halide fine grains containing silver iodide or an iodide-releasing compound is used.
However, in the method wherein an aqueous iodide solution is used, by adding iodide ions in the free state into a reaction solution, a nonuniform region is produced in which the concentration distribution of iodide ions is nonuniform. Therefore, uniform growth of grains cannot take place from grain to grain.
On the other hand, the technique disclosed in the above-mentioned patent application is a technique wherein iodide ions are released slowly to grow grains uniformly without a change in the halogen composition (the microscopical distribution of silver iodide) in the grains and from grain so grain. However, even when silver halide grains are formed by using the exemplified compounds of iodide-ion-releasing compounds described in the above-mentioned patent application, the method does not satisfactory meek the demand for lowering of fogging, high sensitivity, and improvement in abrasion-and-pressure resistance.